PTSD among women is a particularly pernicious and chronic disorder associated with significant psychiatric comorbidity, high rates of suicidality, substance abuse, self-injury and multiple traumatization including repeated sexual assault and domestic violence. Public-sector mental health services are the disproportionate recipient of traumatized women with between 62% to 98% of treatment seeking women reporting a history of trauma and of those, up to 40% carry a diagnosis of PTSD with various comorbidities. Over 40 single-site randomized trials of cognitive-behavioral therapy for PTSD have been conducted. However, to date, there are only two large-sample randomized clinical trials which have evaluated the effectiveness of such treatments in the community and both of them concerned military populations. This application proposes to evaluate the effectiveness of an evidence-based PTSD treatment in the context of a collaborative partnership of four public mental health clinics serving diverse populations. The intervention is a two module, sequential treatment (STAIR/MPE) in which the first module emphasizes present-focused skills training in affective an interpersonal regulation (STAIR) for day-to-day life difficulties and the second module incorporates past-focused work on the processing of the trauma, using a modified version of prolonged exposure (MPE). This cognitive behavioral treatment was specifically designed to treat high risk, multiply traumatized women with chronic PTSD and has been demonstrated to provide significant and clinically substantial relief from PTSD as well as improvement in emotion management and interpersonal functioning. We will assess the effectiveness of STAIR/MPE compared to Treatment as Usual (TAU) in the context of every day clinical care. The study is a randomized, controlled repeated measures intent-to-treat design to assess STAIR/MPE as compared to TAU at post-treatment and three and six-month follow-up. Four sites (Western Ontario, Boston, New York and Atlanta), each situated within a large public sector mental health network, will enroll 88 treatment-seeking women with PTSD related to interpersonal violence yielding a total of 352 study participants. The primary outcome will be PTSD symptom severity. Secondary outcomes will be negative mood regulation self-efficacy, interpersonal problems and general level of psychiatric impairment (GAF scores). Exploratory aims include the examination of the relationship between variations in treatment implementation and treatment outcome as well as the influence of patient characteristics and other contextual (therapist and organization) variables likely to impact implementation. We will also introduce web-based technology as a resource intended to strengthen clinical networks and maintain use of study materials after the trial has ended.